Our broad objective is to understand the molecular mechanisms of neuropeptides involved in the development and maintenance of androgen-independent prostate cancer (PC). Our underlying hypothesis is that neuropeptides synergize with low levels of androgen via G-protein coupled receptor signaling to activate androgen receptor (AR) signaling that contribute to the development of androgen-independent PC. Neuropeptides such as bombesin and endothelin-1 (ET-1) have been implicated in PC progression. In addition, recent studies suggest that AR-regulated genes enhance androgen-independent PC growth in relative androgen absence through AR-dependent mechanisms, i.e., that AR itself mediates androgen-independent progression. Our preliminary studies indicate that bombesin and ET-1 can synergize with castrate levels of androgen to induce transcriptional activation of androgen-responsive genes as well as phosphorylation of the AR, and that ET-1 together with low dose androgen can increase AR protein expression. These data suggest that neuropeptide signaling can influence AR transcriptional activation. Based on these data, in this revised application our specific aims are 1) to determine the molecular basis for neuropeptide growth factors contributing to the development of androgen-independent PC and the effects of neuropetides on AR signaling; and 2) to determine the molecular mechanisms by which neuropeptides potentiate androgen receptor-mediated transcriptional activation and AR amplification. These aims will be accomplished by defining the effects of bombesin and ET-1 on AR signaling, AR phosphorylation, AR autoregulation, and AR co-factors. These studies will enable us to better determine the function of neuropeptides in PC cells, to explore the cross-talk between neuropeptides and AR pathways, and to gain a better understanding of the function of neuropeptides in the development and progression of PC. Moreover, understanding the interaction between AR and neuropeptides, and the cross-talk between neuropeptide and AR signaling pathways will help to clarify the potential use of new therapeutic agents which can effectively interfere with or inhibit the effects of neuropeptides in the development of hormone refractory PC after anti-androgen therapy.